With greens environmental protection and low-carbon economy concepts becomes deeply rooted among the people continuously around the world, requirements of operators for reduction of power consumption of a wireless communication system also become increasing high. In the wireless communication system, a Radio Frequency (RF) power amplifier (power amplifier for short) in a base station device is one of core modules of the whole system, and an important index of the RF power amplifier is the efficiency of the power amplifier. It is indicated from data analysis that in the whole base station device, the energy consumption of the power amplifier portion accounts for about 60% of the overall energy consumption, and therefore, enhancing the efficiency of the power amplifier becomes most efficient means to reduce the power consumption of the base station device and reduce the operator's Operating Expense (OPEX). Therefore, in the face of the increasingly intensive market competition for wireless communications, high efficient RF power amplifier technologies have become one of focuses of competition in the wireless communication industry.
A Doherty power amplifier is a high efficient power amplifier technology which is the most widely applied currently in the wireless communication system, and was invented by a U.S. Electronics Engineer named William H. Doherty in 1936. However, in the next about thirty years, people diverted their attention. Until the late 1960s, with the development of the communications technology, especially of the satellite communications, the problem of the efficiency and linearity of the power amplifier was re-submitted in a new historical occasion, and the Doherty amplifier was excavated again and was widely used in communication and broadcasting systems in the 1970s. At present, the Doherty power amplifier is applied with the Digital Pre-Distortion (DPD) technology, and has become a mainstream architecture form of a high efficient power amplifier of a base station in a wireless communication system.
The basic idea of the Doherty power amplifier is an active load-pull, and the principle of a conventional Doherty power amplifier is shown in FIG. 1, a conventional Doherty power amplifier primarily comprises a drive stage amplifier (Dr1 . . . Drn in the figure), a power splitter (D in the figure), a carrier amplifier (C in the figure, which is also referred to as a main power amplifier), a peak amplifier (P in the figure, which is also referred to as an auxiliary power amplifier), a power combination circuit (Combiner in the figure), etc. Wherein, the carrier power amplifier operates in class B or AB, and the peak power amplifier operates in class C. Both bear different input signal powers respectively, and need to make their power amplifiers operate in respective saturation areas as much as possible, thus ensuring that the whole power amplifier maintains a high efficiency in a large range of the input signal power as much as possible, and meanwhile ensuring a certain linearity.
The Doherty power amplifier primarily comprises the following three operating states:
small signal area. When the input signal is small, the peak amplifier is in an off state, and the carrier amplifier operates in class AB, and at this time, the carrier amplifier operates in a matching state with a maximum efficiency;
load modulation area. When the input signal increases to a certain extent, the carrier amplifier gradually transitions from an amplification area to a saturation area, and the peak amplifier gradually transitions from a cut-off area to the amplification area, and at this time, the load of the carrier amplifier and the peak amplifier are both unstable, and the load impendence changes with the power; and
saturation area. With the continuous increase of the input signal, both the carrier amplifier and the peak amplifier finally operate in the saturation state, and both correspond to a 50Ω load, and the output powers are added.